Far Out Space Propulsion Conference Blasts Off

Far Out Propulsion Conference
Blasts Off

Advanced Propulsion Research Conference
opens today in Huntsville

April 6, 1999:
Atoms locked in snow, a teaspoon from the heart of the sun,
and the stuff that drives a starship will be on the agenda of
an advanced space propulsion conference that opens today in Huntsville.

Right: A fusion-powered spaceship starts braking into
orbit around Titan, Saturn's methane-shrouded moon and a possible
harbor for extraterrestrial life. Basic research on fusion rocket
technology is one of several topics for this week's workshop.
(NASA/Marshall)

The tenth annual Advanced Propulsion Research Workshop will
be held at the University of Alabama Tuesday through Thursday.
It's sponsored by NASA, Marshall Space Flight Center, the Jet
Propulsion Laboratory, and the American Institute of Aeronautics
and Astronautics.

Today, travel to other planets follows the New England
farmer's cautionary note: "You can't get there from here."
In other words, you have to go someplace else. That first stop
is low Earth orbit, followed by a boost that puts a probe on
a long arc to its destination. Sometimes, the probe goes in the
"wrong" direction, like the Cassini mission to Saturn
which first is making "gravity slingshot" passes by
Venus and the Earth as the price of using a conventional rocket
to leave the ground.

Improving conventional rockets is one of the
near-term steps sponsored by NASA/Marshall. In a sense, rockets
are batteries comprising chemicals that have been prepared and
stored so they hold a tremendous amount of potential energy.
Pack more energy into a smaller volume, and you can send heavier
probes deeper into space, and faster. The challenge is reaching
beyond the sophisticated fires that we have now. The Space Shuttle
Main Engines, for example, burn oxygen and hydrogen stored in
liquid form. Its Solid Rocket Boosters burn aluminum and oxygen
locked in a rubbery compound.

"One of the
areas we're studying, at Glenn Research Center, is solid hydrogen
and atoms," explained John Cole, a manager in the Advanced
Space Transportation Project office at NASA/Marshall. "You
can get as much as 10 times as much energy out as you would from
conventional combustion." Cole will review Marshall-sponsored
research during this morning's opening session.

Left: Advanced plasma engines that produce high-power
jets of ionized gas are another option for travel to the planets.
(NASA/Marshall)

Other Propulsion
Stories this week

Apr 6: Ion Propulsion -- 50 Years in the Making
-
The concept of ion propulsion,
currently being demonstrated on the Deep Space 1 mission, goes
back to the very beginning of NASA and beyond. April
6:
Far
Out Space Propulsion Conference Blasts Off - Atoms locked in snow, a teaspoon from the heart
of the sun, and the stuff that drives a starship will be on the
agenda of an advanced space propulsion conference that opens
today in Huntsville.April 7: Darwinian
Design - Survival of
the Fittest SpacecraftApril 7: Coach-class
tickets for space? - Scientists
discuss new ideas for high-performance, low-cost space transportationApril 8: Setting
Sail for the Stars - Cracking
the whip and unfurling gray sails are among new techniques under
discussion at the 1999 Advanced Propulsion Research WorkshopApril 12: Reaching
for the stars - Scientists
examine using antimatter and fusion to propel future spacecraft.April 16:
Riding
the Highways of Light - Science
mimics science fiction as a Rensselaer Professor builds and tests
a working model flying disc. The disc, or "Lightcraft,"
is an early prototype for Earth-friendly spacecraft of the future.Â

Many atoms prefer to join with their own kind to form
molecules. When they join, the surrender a tremendous amount
of energy. If they are cold enough, they won't join, so NASA
is experimenting with methods to separate carbon or boron molecules
into atoms, then trap them in hydrogen ice pellets. The ice,
in turn, would float in liquid helium.

Cole said this slushlike mix
is unstable, and requires several years of work before test engines
could be built. But if successful, it would yield an engine with
a specific impulse - a measure of efficiency - of 750 seconds.
The Shuttle Main Engine produces 455 seconds.

Another way to enhance chemical rockets is with "strained
ring hydrocarbons," Cole explained. Benzene burns quite
well because it's built around rings of six carbon atoms. Taking
three carbon atoms out produces bicyclopropylidene that has even
greater potential energy.

"It's amazingly stable," Cole noted, "so it's
not shock sensitive." Its value is not in higher energy
- a bicyclopropylidene is only 5 percent more efficient than
the refined kerosene used as a first-stage fuel in many rockets
- but its greater density - more than double.

"This is very dense, so it doesn't take much tank mass
to carry the propellants," Cole continued. It also reduces
the size of the tank, so there's less surface area to push through
the dense lower atmosphere at liftoff.

The atmosphere itself
would be pressed into service with a radical concept being tested
by Prof. Leik Myrabo of Renssalaer Polytechnic Institute in a
project jointly sponsored by NASA/Marshall and the Air Force
Research Laboratory at Edwards Air Force Base, Calif. The Lightcraft
would rise on a series of hot air pulses produced by a high-energy
laser.

The laser beam would be focused just aft of the Lightcraft
and superheat the air, which expands, pushing the craft upward.
Slots in the craft's skirt push more air into the now-empty region
and another pulse of light pushes the craft a little farther.
A 15-cm (6 in.) diameter model has been tested in brief flights
at the White Sands Missile Range at White Sands, N.M.

Left: Hoisted by a series of
air bursts, a 15 cm-diameter test model of the Lightcraft rises
in a hangar at White Sands Missile Range. The air is heated by
a high-energy laser and focused into a small area just aft of
the craft. (Renssalaer Polytechnic Institute)

An advanced version of the Lightcraft
would be a large helium-filled balloon that focuses microwaves
beamed from the ground or space. The balloon would be ringed
by ion engines that would electrify the air to push the craft
upwards.

"It's a technical stretch in a lot of areas," Cole
admits.

Advanced technologies for nuclear propulsion also are under
study.

"If NASA decides to send people to Mars with a nuclear
rocket, we want to make sure that the rocket is as safe as possible,
and perhaps to improve the performance," Cole said.

The simplest nuclear rocket would pump liquid hydrogen over
a reactor core, and expel the superhot gas out a rocket nozzle.
Cole said the University of Florida is studying high-temperature,
high-strength alloys that would withstand the extreme temperature
difference.

NASA/Glenn is studying
an intriguing variation that would give a nuclear rocket the
equivalent of a military jet's afterburner. In this scheme, liquid
oxygen would be pumped into the exhaust nozzle. This would help
cool the hydrogen enough that it could burn, combining with the
oxygen to form water vapor.

Left and below right: The plasma mirror experiments at NASA/Marshall
are intended to understand the basic technologies for containing
the superhot gases in a fusion plasma, and then release just
enough of the energy to propel a rocket. (NASA/Marshall)

A more powerful
rocket would use nuclear fusion, the same power source at the
heart of the sun. Controlled fusion - combining the nuclei of
two lightweight atoms and reaping energy from the process - has
eluded the best efforts of scientists and engineers since an
early attempt in the late 1930s.

(In the 1930s, Arthur Kantrowitz, then with the National Advisory
Council for Aeronautics - NASA's predecessor - made the known
fusion attempt at Langley Field Station, now Langley Research
Center. Kantrowitz and several colleagues rigged a pressure vessel
normally used with a wind tunnel and tried to produce controlled
fusion. They were far below the necessary pressures and temperatures
needed, but it does mark the first attempt. It was described
several years ago in American Heritage Invention & Technology.)

"It is not NASA's intent
to solve fusion power production problems," Cole said. "We're
trying to understand enough of the physics to understand typical
plasmas that might be used in propulsion. That way, we'll be
ready to take advantage of fusion whenever the problem is solved."

Cole said that solving this problem is essential to large
missions - including manned - to the outer planets."Mars
is as far as we can go because the trip time is too long,"
Cole said, "unless we get specific impulses of 50,000 to
100,000 seconds." That's more than 200 times the efficiency
of the Shuttle Main Engine, although the thrust would be lower
and the fusion engine would fire for weeks at a time.

"Fusion could get us to the outer planets - and perhaps
so could antimatter," Cole continued.

Antimatter is the
stuff that powers fictional starships, but NASA is not planning
to reach warp speeds with it. Again, the antimatter would be
like a battery storing energy on Earth for later use in space.
When expended, the antimatter would combine with matter to superheat
a gas that would be expelled out a nozzle to power the spaceship.

Left: Yes, it really does resemble a flying saucer.
Faculty and students at Renssalaer Polytechnic Institute in Troy,
N.Y., are designing an advanced Lightcraft concept that would
use microwave energy beamed to the saucer and converted to electricity
to drive magnetohydrodynamic engines that would heat air and
propel the craft. (Renssalaer Polytechnic Institute)

And if you thought antimatter propulsion wasn't far-enough
out on the research frontier, Mark Millis of NASA/Glenn will
review the Breakthrough Physics program that is investigating
some subtle and genuinely odd aspects of quantum physics that
might be exploited in the next millennium for propulsion.

Spacecraft
may fly on "empty"
(Jan. 22, 1999) Using a propulsive tether concept, spacecraft
may be able to brake or boost their orbits without using onboard
fuel. A NASA/Marshall project, named "ProSEDS," is
slated to demonstrate braking, by accelerating an expended rocket
toward re-entry.